Method of making seamless tubes



iiov. 1932. J w -r 1,888,607

METHOD OF MAKING SEAMLESS TUBES Filed April 6, 1929 A x T 0 1&4.

l4 l5 l6 Jig! Jafi/v M OFFUTT) 6 pal object Patented Nov. 22, 1932UNITED STATES PATENT OFFICE JOHN W. OFFUTT, OF ELLWOOD CITY,PENNSYLVANIA, ASSIGNOR TO NATIONAL TUBE COMPANY, A CORPORATION OF NEWJERSEY METHOD OF MAKING SEAM'LESS TUBES Application filed April 6, 1929.Serial No. 353,175.

This invention relates to the manufacture of seamless butt and/or lapweld tubes and also electrically welded pipes and tubes and, while notlimited thereto, has for its princithe provision of a novel methodwhereby tubes of small diameter (i. e., materially less than threeinches diameter) having the thin wall thickness or gage suitable forcommercial use are made in a rapid,

l economical and eflicieut manner.

Heretofore small diameter tubes such as from one-eighth to one inch pipesizes, when not made by the butt-weld process, have been cold drawn fromlarger sizes of hot rolled seamlem tubes.

In the manufacture of seamless tubing it v has heretofore not been foundpracticable to produce hot rolled tubes of thin enough gage to be ofcommercial diameter. In piercing a solid round or billet of circularcross-section by the universally used rotary piercing mill, it is foundthat a round billet or blank of about three inches diameter is about thesmallest size that can be commercially worked. This limitation indiameter is fixed by the size of the piercing mandrel which must have adiameter large enough to resist the end thrust imposed upon it in thepiercing operation. A similar limitation is also set on the minimum sizeof the pierced billet that can be successfully rolled in the plug milland then reeled in two operations subsequent to the piercing operation.

It is well established that all seamless tub s of a finished size ofless than three inches di ameter must be passed through a sinking millafter the plug rolling and reeling operations to reduce the reeled tubesto the desired diameter.

As is well known, a sinking mill isa continuous universal mill havinggrooved rolls. with the grooves in each successive stand of rollssmaller than those in the preceding stand. The grooves in the firststand are slightly less in diamcterthan the reeled tube and the groovesin the last stand are of the diameter of the completed tube The rollstands, of which from eight to twenty-four may be used, are arranged intandem and wall thickness and y 23 of less than one and OIl-Q-llfllf totwo inches are usuallyspaced as closely together as their constructionwill permit. The spacing will vary from thirty inches to as much as fivefeet, center to center.

The'tube, while being passed through the sinking mill, does not haveasupporting man- 'drel on its interior so that the reduction in itsdiameter is accompanied by thickening of the tube wall; In order toprevent, as far as possible, this'increase in wall thickness therelative roll speeds of the successive roll stands are adjusted tocreate a pull on the tube between the rolls, which results in stretchingthe tube. Most-of the reduction'due to the stretching operations is inwall thickness and there is very little, if any, reduction in diameter;the result is, that the amount the wall of the tube is thickened in thesinking mill is lessened. i

It is found, however, that when reduced in diameter in a sinking milland with the roll speeds adjusted for stretching, the tubes are materialheavier in gage on their ends than in the middle. This thickening, whichis of marked degree, extends for a distance from each end about equal totwice the distance between roll stands. This is because no pull can beexerted on a given section of its length unless the tube is grippedsimultaneously between two or nore pairs of rolls, a condition that doesnot exist when the tube is entering or leaving the roll train formingthe sinking mill.

That is to say, there can be no stretching until after'the front end ofthe tube has entered the second stand of the rolls and there will benone after the rear end emerges from next to the last stand.

In practice up to the present, the increment in roll speeds onsuccessive stands as heretofore arranged has been proportioned rathercloselv to the. reduction of area. due to the reduction in diameter lessthe natural thickening of the tube walls. in order for the tubcs to beof uniform gage from end to end. This also means that the gage of thetube as rolled prior to the sinking operation must be considerablylighter than the desired gage or wall thickness of the finished tube.Since there is a practical limit to the lightness of gage of the tubewhich can be rolled and reeled prior to the sinking operation, theminimum gage of the finished tube after sinking is regulated orcontrolled by the minimum gage which can be rolled on the plug millprior to the sinking operation.

I have demonstrated by actual trials that by increasing the differencein the speeds of the successive stands of rolls enough stretching can beaccomplished to cause a material reduction in the diameter of the tubesand that at the same time the wall of the tubes not only can be heldagainst thickening but, when desired, can even be reduced in thickness.In obtaining these results the rolls of the mill are made small indiameter and the roll stands are spaced very closely, center to centerof stands, this close spacing being for the purpose of lessening to aminimum the length of the end portions of thetubes that have thethickened gage at the completion of the sinking operation. It always isnecessary to crop and discard these thickened ends as scrap, hence theimportance of keeping them as short as possible.

Referring now to the drawing forming part of this specification, Figure1 is a diagrammatic plan of a standard sinking mill as used in sinkingthe rolled and reeled tubes.

Figure 2 is a section through a length of tube which has been stopped inthe sinking mill of Figure 1, and shows the several reduc-.

tions as made at dilferent points in the length of the tube in passingthrough the sinking mill of Figure 1.

Figure 3 is a view similar to Figure 1, showing the modified sinkingmill used in carrying out the final rolling steps of this novel method.

Figure 4 is a View similar to Figure 2, showing a length of tubewhich'has been stopped in the mill of Figure 3 to illustrate thereductions made simultaneously at different points in the length of thetube in its passage through the second sinking mill.

Figure 5 is a sectional plan of a tube illustrating the length of thecrop ends relative to the length of finished tubes made in accordancewith my improved method.

In making tubes by my improved method, a tubular blank designated by theletter A, which has been produced by piercing a round billet or bycasting or in any other approved manner after being heated, is firstrolled in a plug mill and is then reeled in the usual way. tubular blankA is greatly elongated and ,is correspondingly reduced in wall thicknessand outer diameter. Owing toits being rolled over a plug, the innerdiameter of the hollow blank is not materially changed in the plugrolling operation.

After being rolled in the plug mill, the billet or blank is then passedthrough the In the plug rolling operation, the

things, upon the amount of increasei'n the diameter of the tube thatresults from the reeling operation.

However, the reeling step as ordinarily performed is comparable to anironing operation whereby scratches and scores and other irregularitieson the inner and outer surfaces of the tube are lessened and removed,and variations in wall thickness at different points in the length of atube, that result from the piercing and later plug rolling operations,are equalized in the reeling operation. In some cases, the reeling stepmay be omitted and the plug rolled tubes passed directly. to the sinkingmill.

In the manufacture of seamless tubes of the small sizes and thin wallsthat are made possible by using my improved method, two sinking mills,or, what is the same thing, a sinking mill comprising two separate anddistinct units B and C will be employed. In the first unit B, whichcomprises a sinklng mill of existant and well known type, the reeledtube is increased in length and is reduced in diameter and to a gage orwall thickness which, while uniform throughout its length, is thickerthan that of the tube at the completion of the reeling operation. Thetube becomes thickened in gage or wall thickness because a mandrel orother support for the inside of the tube is not employed in the sinkingoperation.

The tube 'then passes from the first unit B of the sinking mill into thesecond unit C. In this operation it is further rolled and also isstretched to a considerable extent while being rolled, its outerdiameter being reduced in this operation so as to lessen the gage orwall thickness of the tube to that or somewhat less than that of thetube after completion of the reeling operation prior to its entering theseries of sets of rolls forming the first unit B of the sinking mill.

The tube, when rolled in the second sinking mill, isstretched to a veryconsiderable extent because of the pulling action of each set in thesuccessive sets of rolls forming the second unit C of the sinking mill.It will be obvious that because of the close spacing between the rollstands that, in comparison with the total length of the tube, only asmall portion of its length, at each of its ing small seamless ends,will not be stretched, with the result that the small unstretchedportion at each end of the tube will be of the same or somewhat greaterwall thickness than the intermediate stretched portion, and that theunstretched end portions will be of such small proportion of the totallength of the tube as to permit of cropping the thickened end portionsand discarding them as scrap Without a prohibitive scrap loss.

As tubes made by my improved method will be from fifty to one hundred ormore feet in length instead of a maximum of from thirty to forty feet,and as the leng h nec essary to cut off the ends of the tubes to removethe thickened portions is comparatively short, say five per cent, I amenabled to make seamless tubes of small diameter and thin wall with ascrap loss so small as to make the method practicable on a commercialscale.

While I have shown one arrangement of apparatus and have described acertain specific order of steps for carrying out my novel method, itwill be understood that I do not wish to be limited thereto sincevarious mcd'fications may be made without departing from the scopethereof, as defined in the appended claims. While this invention isparticularly well adapted for use in maktubes, it also is intended foruse in'the manufacture of pipes or tubes of any diameter or size.

I claim- 1. The method of making seamless tubes which consists informing a seamless tube blank by rolling and reeling to a diameter materially larger than a wall thickness approximating that of the finishedtube, then subjecting the tube to a sinking operation to reduce itsdiameter and increase its wall thickness and form a tube having asubstantially uniform wall thickness, and then subjecting the tube to asecond combined sinking and stretching operation in which the tube wallsare stretched by an amount sufficient to reduce the thickness of thewalls to a greater extent than they are thickened by the first sinkingoperation, whereby a finished tube is formed of a materially lessdiameter and a thinner wall than the blank when entering the combinedsinking and stretching operation.

2. The method of making hot rolled small diameter seamless tubes whichconsists in forming a seamless tube blank by rolling and reeling to adiameter materially larger than that of the finished tube and arelatively thin wall, then subjecting said tube to a combined sinkingand stretching operation so as to reduce its diameter and increase itswall thickness, forming a tube having a substantially uniform wallthickness, and then subjecting said tube to a second combined sinkingand stretching operation in which the tube walls are stretched asufficient amount to reing it in duce the thickness of said walls agreater amount than they are thickened by the last sinking operationwhereby a finished tube is formed having a materially less diameter thanthe blank and a thinner wall than that entering said last combinedsinking and stretching operation.

3. The method of making hot rolled small diameter seamles tubes whichconsists in forming a seamless tube blank by the usual rolling andreeling steps having a diameter materially larger than the finished tubeand a wall thickness approximating that of the finished tube thensubjecting said tube to a combined si ing and stretching operation so asto reduce its diameter and increase its wall thickness, forming a tubehaving a substantially uniform wall thickness, and then subjecting saidtube to a second combined sinking and stretching operation in which thetube walls are stretched a sufiicient amount to reduce the thickness ofsaid walls an amount equal at least to the increased thickness formed byboth sinking operations, whereby a finished tube is formed having amaterially less diameter than the tube when entering said last combinedsinking and stretching operation and a wall thickness at least as thinas the original rolled and reeled blank.

4. In the manufacture of seamless tubes,

the steps including increasing the wall thickness and length of atubular blank while decreasing its inner and outer diameters by rollasinking mill, and then lessening theouter materially increasing thelength of the blank in said rolling operation by rolling it in a secondsinking mill, and stretching the blank in rolling it in the secondsinking mill.

5. In the manufacture of seamless tubes, the steps includin increasingthe wall thickness and length 0% creasing its inner and outer diametersby rolling it in a sinking mill, and then lessening the outer diameterand Wall thickness of the blank Without increasing its inner materiallyincreasing itslen th by rolling it in another sinking mill an stretchingthe blank in rolling it in the second sinking mill.

6. In themanufacture of seamless tubes, the steps including materiallychanging the wall thickness and length of a tubular blank whiledecreasing its inner and outer diameters by rolling it in a sinkingmill, and then lessening the outer diameter and wall thickness of theblank without materially changing its inner diameter and materiallyincreasing its length by rolling it in another sinking mill andstretching the blank in rolling it in the second sinking mill.

7. The method of making hot rolled tubes which consists in forming atubular blank having a diameter and a wall thickness materially greaterthan the diameter and wall thickness of the finished tube, thensubjecting diameter and wall thickness and diameter and ins a tubularblank while dethe heated blank to a combined sinking and stretchingoperation so as to reduce its diameter without increasing its wallthickness and form a tube having a substantially uniform wall thickness,and then subjecting the tube to a second combined sinking and stretchingoperation in which the stretching forces predominate over the sinkingforces and the tube Walls are reduced in thickness an amount suflicientto provide a finished tube having a materially less diameter than thetube when entering the last combined sinking and stretching operationand a Wall thickness niaterially less than the originally rolled tube.

8. In the manufacture of tubes, the steps including increasing the wallthickness and length of a tubular blank while decreasing its inner andouter diameters by rolling it in a sinking mill, and thenlesSening-tIie-JOuter diameter and wall thickness and materiallyincreasing the length of the blank in said rolling operation by rollingit in a second sinking mill, and stretching the blank in rolling it inthe second sinking mill.

9.'In the manufacture of tubes, the steps including increasing the wallthickness and 'length'of a tubular blank while decreasing its inner andouter diameters by rolling it in a sinking'mill, and then lessening theouter j diameter and Wall thickness of the blank without increasing itsinner diameter and materially increasing itslength byrolling it inanother sinking mill and s'tret'ching the blank in rolling it in thesecond sinking mill.

10. In the manufacture of tubes, the steps including materially changingthe; wall thickness and length of a tubular blank while 1 decreasing itsinner and outer diameters by rolling it in a sinkingniill, and thenlessening the outer diameter and Wall thickness of; the blank withoutmaterially changing its inner diameter and materially increasing itslength by rolling it in another sinking mill and stretching the blank inrolling it in the I second sinking mill. y

11. The method of making tubes which ineludes the step of subjecting aheated tubularblank to a combined sinking and stretching operation inwhich the stretching forces predominate over the sinking forces anamount suflicient to more than counteract-the tendency of said sinkingforces to thicken the tube walls, whereby the diameter of the blank isreduced and its length increased and its wall thickness is reduced toless than the wall thickness of the original tubular blank.

In testimony whereof, I have hereunto set my hand.

' JOHN IV. OFF UTT.

